Recognizing the negative effects of fats, oil and grease (FOG) on sewer systems and/or waste water treatment plants, it is important to inhibit FOG from entering into wastewater collection systems and/or landfill sites. Communities, counties, and water districts are grappling with the issue of how best to handle grease trap wastes. EPA estimates that about one half of all the municipal sewer clogs are the result of FOG building up in the sewer pipes. Most wastewater treatment plant managers feel that from a technical point of view, it is best to have regulations requiring restaurants to have grease traps pumped regularly, and to have the waste discharged at wastewater treatment plants where it can be properly treated and disposed of. Thus, there are grease trap pumping companies that are paid to collect the waste and paid to dump the collected FOG at facilities that can convert such FOG containing waste to inert solids or convert to useable materials such as biogas, biodiesel, biological fertilizer, etc.
Biodiesel is a diesel replacement fuel for compression-ignition (CI) engines and is a legally registered fuel and fuel additive with the U.S. Environmental Protection Agency (EPA). The EPA registration includes all biodiesel that meets the ASTM specification ASTM D 6751 and such standards do not depend on the oil or fat used to produce the biodiesel or the specific production process employed.
The biodiesel manufacturing process converts oils and fats into chemicals called long-chain mono-alkyl esters or biodiesel. These chemicals are also referred to as fatty acid methyl esters (FAME). The term mono-alkyl ester indicates that biodiesel contains only one ester linkage in each molecule. Biodiesel fuel can be produced from a variety of oils and fats such as plant oils, recycled cooking grease or oil (yellow grease) and animal fats. Animal fats may include all types of tallow, lard, yellow grease, poultry fats and fish oils. Plant oils may include, corn, canola, sunflower, rapeseed, cottonseed, etc. Biodiesel is produced through a chemical reaction of a triglycerides (TG) or free fatty acids (FFA) with an alcohol, such as methanol, to form an alkyl ester. Free fatty acids, which are found in degraded oils such as FOG, can be converted using an acid catalyst. Triglycerides can be converted using an alkaline catalyst.
Included in the grouping for conversion to biodiesel are recycled greases, such as cooking oils and restaurant frying oils. Brown grease is a material, either liquid or solid, composed primarily of fats, oils and grease from animal or vegetable sources. Yellow grease is oil and grease that comes directly from fryers and other cooking equipment. Trap grease or brown grease is waste that is recovered from grease traps and interceptors. A grease trap is a small volume device located inside a food service facility, generally under a sink, designed to collect, contain, or remove food wastes and brown grease from the waste stream while allowing the balance of the liquid waste to discharge into the wastewater collection system, usually a sanitary sewer system. A grease interceptor is a large volume device located underground and outside of a food service facility designed to collect, contain or remove food wastes and brown grease from the waste stream while allowing the balance of the liquid waste to discharge to the wastewater collection system, usually a sanitary sewer system.
Grease from meat packing houses and slaughter houses must also be addressed. It is graded according to color as white, yellow, or brown grease. White and yellow packing-house greases commonly contain only hog fat. Brown grease may also contain some beef and mutton fat, for it includes the fat from the catch basins. In large packing houses great quantities of water are used which ultimately find their way into the sewers, carrying along in their passage not inappreciable quantities of fats. To recover these it is customary to let the waters settle in basins before they finally flow into the sewer. In these basins fat rises to the surface; it is then skimmed off and combined with the brown grease. Such recovered greases may be used in the manufacture of biodiesel fuels, soap, candles, lubricants and certainly included in some types of animal feed. As such, recovering a substantial portion is important not only as a value added product but also to prevent entry into sewer systems.
In light of the above discussion, there is a need for separation systems that can effectively separate dispersed FOG from emulsions and separate free-floating FOG from a waste stream to provide dewatered emulsions and separated fats, oils and greases thereby providing value added separated product while producing a minimal amount of negative effects on sewer systems, wastewater treatment facilities and/or landfill sites.